Based on previous experience with high-speed, short-range midget submarines, Number 71 displaced only 230 tons surfaced with a length of 140 ft (43 m).

[2] By late 1942 it had become apparent to the IJN that conventional submarines were unable to survive the new ASW techniques coming into service, such as radar, HF/DF, sonar, and new depth charge projectors.

It featured powerful electric motors, streamlined all-welded hulls, and a large capacity battery consisting of 4,192 cells.

The I-201s, like other Japanese submarines of the period,[5] were also equipped with a crude snorkel, allowing underwater diesel operation while recharging batteries.

The submarine was designed for mass production, with large sections prefabricated in factories and transported to the slip for final assembly.

They were part of a group of four captured submarines, including the giant I-400 and I-401, which were sailed to Hawaii by US Navy technicians for further inspection.

On 26 March 1946, the US Navy decided to scuttle these captured Japanese submarines to prevent the technology from falling into the hands of the Soviet Union.